1. Field of the Invention
The present invention relates to a dynamic quantity sensor.
2. Description of Related Art
JP-A-2006-98168 or JP-A-2000-9471 discloses a dynamic quantity sensor having a sensor chip for detecting an angular velocity or acceleration. The sensor chip is made of a semiconductor chip including a detector, and the detector has a movable part and a fixed part. The movable part is displaced when a dynamic quantity, e.g., angular velocity or acceleration, is applied thereto. The fixed part opposes to the movable part, and the dynamic quantity can be calculated by a variation of a capacitance between the movable part and the fixed part. Typically, the sensor chip is mounted on a circuit chip, i.e., substrate, and a soft adhesion layer is disposed between the circuit chip and the sensor chip, so that a thermal strain (distortion) can be reduced.
In contrast, in JP-A-2001-217280, a semiconductor chip, e.g., IC chip, is mounted on a circuit chip by using a face-down mounting, and the semiconductor chip and the circuit chip are connected through a bump made of gold, for example.
Here, with reference to the above-described documents, the sensor chip for detecting the dynamic quantity is mounted on the substrate through the bump. At this time, a pad of the sensor chip and the substrate are connected to each other through the bump.
The sensor chip has a rectangular board shape, and the detector of the sensor chip is arranged at an approximately center position of the sensor chip. Plural pads of the sensor chip are arranged at corners of the sensor chip, respectively. That is, the plural pads are arranged outside of the detector. Therefore, when the sensor chip is connected to the substrate through the bump, the corners of the sensor chip are fixed to the substrate through the bump.
Here, when the substrate and the sensor chip are connected by the bump, stress generated by a thermal strain or sensor assembling may be directly transmitted to the sensor chip, because the bump is made of a rigid material, e.g., gold. At this time, the sensor chip may be deformed, as shown in FIGS. 7A, 7B and 7C.
Further, the dynamic quantity sensor typically includes a plurality of the detectors in the single sensor chip. If the capacitance of the detector is varied by an external disturbance, the capacitance variation generated by the external disturbance has to be eliminated by calculating a differential output of the capacitances among the plural detectors, in order to provide a target capacitance variation.
Here, as shown in FIGS. 7A and 7B, when a sensor chip 100 is deformed in a predetermined direction, e.g., X-axis or Y-axis, the capacitance variation generated by the external disturbance can be eliminated by using the differential output. However, as shown in FIG. 7C, when the sensor chip 100 is distortedly deformed, the capacitance variation generated by the external disturbance cannot be eliminated, so that a sensor characteristic, e.g., temperature characteristic, of the dynamic quantity sensor may be affected.